Portable polarographic half cell



April 19, 1955 R. K. LADISCH 2,706,711

PORTABLE POLAROGRAPHIC HALF CELL Filed Aug. 12, 1953 2 Sheets-Sheet lFRITTEDI GLASS INVENTOR fiOZf/iarl Ladiscfi ATTORNEY April 19, 1955 R.K. LADISCH PORTABLE POLAROGRAPHIC HALF CELL 2 Sheets-Sheet 2 Filed Aug.12, 1953 INVENTOR Rolf/Qzrl Ladisck.

mfio 6 0 .2 uw 553 80 0 83 09 0 528 08 0 88 08 0 03 0 00 u H w M Q m H HBY W/ I ATTORNEY United States Patent 1 2,706,711 PORTABLE POLAROGRAPHICHALF CELL Rolf Karl Ladisch, Lansdowne, Pa., assignor to the UnitedStates of America as represented by the Secretary of the Army Theinvention described herein may be manufactured and used by or for theGovernment for governmental purposes without the payment to me of anyroyalty thereon.

The present invention relates to portable polarographic half cells suchas are used in qualitative and quantitative analyses of certainsolutions.

In using a polarograph for studying diffusion currents, a calomel halfcell is commonly employed as a reference electrode in series with thedropping mercury electrode. Half cells in wide use, such as thosedescribed by J. J. Lingane and H. A. Laitinen in Ind. Eng. Chem, Anal.Ed., Vol. 11, p. 504 (1939) and G. S. Smith in The Analyst, Vol. 75, p.215 (1950) cannot be moved about freely because shaking them sometimescauses inaccuracies of 1-3 millivolts or even more, and full accuracymay not be restored until five to six hours have elapsed. Besides, theseprior art structures must be kept in an upright position to maintain theoriginal cleanliness of the platinum contact.

This invention aims to provide a non-polarizable, rugged half cell oflow ohmic resistance, especially made to confine the mercury in a rigidsupport, so that the electrical contact between the platinum wire andthe mercury is not disturbed under the conditions of polarographicprocedure. A specific object is to confine the mercury by material whichis porous to the mercury when the latter is subjected to pressure. Thepreferred porous material is glass frit; when choosing a frit of propersize the area of the mercury can be made equal to or several timeslarger than that of the mercury pool in a conventional half cell.

In the accompanying drawings forming a part of this specification,

Fig. 1 is a full size elevation of the half cell, showing a conventionallead for the platinum wire;

Fig. 2 is an enlarged longitudinal section, omitting the lead;

Figs. 3, 4 and are respectively cross sections on lines 3-3, 44 and 55of Fig. 1;

Fig. 6 is a reproduction of two curves made from actual tests with thehalf cell and a conventional mercury pool electrode; and

Fig. 7 is a diagrammatic sectional view partly in elevation showing aset-up including the half cell for analyzing a solution by polarographicmethods.

Referring particularly to the drawings, Fig. 1 shows the completed halfcell 10 with a lead 11 coupled thereto. The preferred construction(Figs. 2-5) comprises a generally tubular glass body 12 having a tubularfritted glass container 13 enclosed therein. The upper end of container13 is open and has a constricted neck 13a of clear glass fused to theinwardly curved end walls of body 12 to be integral therewith. Theannular space or chamber 14 between container 13 and tubular body 12 isdesigned to hold mercury, shown at 15, the mercury being completelytrapped by the provision of a transverse glass partition 16 closing body12. (The manner in which the mercury is introduced into annular space 14will be described later.) A platinum wire 17 makes electrical contactwith mercury by being fused at 18 into the center of partition 16; wire17 also extends outwardly from the partition. In lieu of a platinumwire, an ordinary tungsten-copper lead may be used. Lead 11 iselectrically connected to the outer end of wire 17 by means of a globuleof soft solder 19. The cupped lower end 20 of body 12 contains a mass ofcement 21 to secure lead 11 against displacement besides insulating thewires. Some of the cement 21 aids in securing a flanged rubber cap 22 onthe cupped end 20. There are several cement compositions which may beused here with satisfactory results. The lower clear glass end oftubular container 13 is closed and may abut the platinum wire 17 asshown, but this is not necessary. Wire 17 may be long enough to reach tothe inner wall of body 12 as shown. Within tubular container 13 a massof calomel paste 23 is placed so that all but the constricted neck ofcontainer 13 is occupied by said paste. The open upper end of container13 is closed by a plug or wad of glass wool 24, or other fibrous inertmaterial may be used to keep the paste within the container.

Referring to Fig. 7, the described half cell has its principal portionimmersed in a sealed cylinder 25 containing KCl solution 26, with asurrounding water jacket 27 having circulating water to keep thetemperature of the cell substantially constant. Also located in thesealed cylinder 25 above the half cell is an open vessel 28 closed atthe lower end by a very thin resin membrane 29 whose under surface is indirect contact with the KCl solution 26. My pending application Ser. No.220,325, filed April 10, 1951, discloses vessel 28 in more detail. Theopen vessel 28 contains the solution to be tested (not shown) and adropping mercury electrode 30 drops mercury 35 in the test solution invessel 28 in the wellknown manner. A battery 31 with a rheostat 32, agalvanometer 33, and a lead 34 to the dropping mercury electrode, arealso shown. The circuit is completed by lead 11 connected to therheostat. As the technique of using the described polarographicapparatus is well understood, no description thereof will be undertaken.

In making the half cell, fritted glass parts with nominal maximum poresizes of 40 microns and 5 microns were used at random. The glass body ofthe half cell was placed in a desiccator and was evacuated by means of ahigh vacuum pump for at least one hour; then with the glass body stillunder vacuum, triple distilled mercury was admitted through a funnel inthe lid of the desiccator in such a fashion that the mercury filled thefritted glass container 13. With frits of 40 microns pore size, themercury penetrated the fritted glass walls of container 13 to occupyannular chamber 14 (as shown in Fig. 2) as soon as the pressure in thedesiccator was restored to atmospheric pressure. With fine frits of 5microns pore size, a pressure of p. s. i. gage from a nitrogen cylinderwas applied to the mercury to accomplish the same result; this latteroperation was performed in a stainless steel bomb, to which the glassbody of the half cell, with the mercury, had been transferred from thedesiccator. After the mercury had been forced to occupy its intendedchamber 14 in the half cell, the excess mercury in container 13 wasshaken off. A paste consisting of mercurous chloride, special forcalomel cells, and potassium chloride solution, special for calomelcells (both of which are procurable on the market) was mixed and wasintroduced into the interior of container 13 to substantially fill it,as shown in Fig. 2. Finally, the open end of container 13 was closed byfibrous glass plug 24.

The potential of the described cell was checked in saturated KClsolution against a saturated calomel electrode. The average deviation ofall cells tested was 0.3 millivolts; these small deviations decreasedeven further after the cells came to equilibrium overnight.

Polarographic analyses of 1.00 millimolar and 2.00 millimolar cadmiumsulfate (reagent grade) in 0.1 normal KCl solution were conducted in aLingane-Laitinen H- cell. The test compartment was separated from thereference electrode by an agar plug as usual. For comparison, aconventional mercury pool-calomel reference electrode in saturated KClsolution was placed in the bottom of the l-l-cell adjacent to the testcompartment, the half cell of the invention being likewise immersed inthe saturated KCl solution above the mercury pool electrode. The surfacearea of the mercury pool was 3.8 sq. cm. In view of the fact that thepotential of the pool electrode may become inaccurate under certainconditions, this electrode was prepared with extreme care, and once ithad been set up in the thermostated H-cell, it was neither removed normechanically disturbed. The pool electrode was renewed wheneversignificant changes in its potential (as measured against a calomelelectrode) became apparent despite the precautions taken. Removal of thetest solution and cleaning of its compartment were done with a suctiontube. The test solution was freed from oxygen by purified nitrogen priorto the analysis, and nitrogen was passed over the solution during theanalysis as is usual. The drop time of the capillary used was checkedduring each run at the half wave potential; it maintained a value of4.89:0.01 sec. The vi W value was found to be 1.83 at an applied potential of 0.700 v. versus SCE, at which the magnitudes of the diffusioncurrents were determined. The capillary cell equipment was kept at i0.lC. by means of a thermostat control. The iR drop across thepolarographic circuit was measured. All data were corrected for the iRdrop and the residual current.

To detect possible time-dependent changes in potential of the describedcell, five curves were drawn consecutively with readings based on thesame test solution. Approximately 45 minutes elapsed between the firstand the last measurements. The heights of the diffusion currents at anapplied voltage of -0.600 v. versus SCE (i. e.,

close to the half wave potential) agreed with each other to better thani0.5 per cent.

Fig. 6 shows the 1 millimolar and 2 millimolar cadmium sulfate curvesobtained with the mercury pool electrode and the described half cell.The values measured for these curves often coincided. The diffusioncurrents measured at an applied potential of -700 mv. with the describedhalf cell were within the ranges of 6.55 :002 microamperes for the 1millimolar solution and 13.05: 0.05 microamperes for the 2 millirnolarsolution. The half wave potentials were read from individual curves foreach reference cell at /2 in (where id is the average diffusion currentin microamperes during the life of the drop of mercury). The readingsagreed among each other within 597:0.5 rnillivolts. The comparativeresistances in ohms were as follows:

Conventitnal Test Solution Hg P031 Half Cell Electrode 1 rnillimolar1,310 l, 230 2 millimolar 1. 160 1,170

The diffusion current constant was calculated on the basis of theoriginal Ilkovic equation with "1 1 being 1.83. (The Ilkovic equation isexplained in Collection of Czechoslovak Chem. Comnm, Vol. 6, p. 498;1934.) The electrolysis was not diffusion controlled, since no maximumsuppressor was present. The value found in this manner for Is was 3.58,which is in very good agreement with the data of Buckley and Taylor(Res. Natl. Bur. Stand, Vol. 34, p. 97; 1945) who obtained 3.54 forcadmium ions in the absence of a maximum suppressor. The half wavepotential of 597 10.5 mv. agrees well with Linganes value of 599:2 mv.(J'. Am. Chem. Soc., Vol. 61, p.

2099; 1939). Attention is directed to the relatively low ohmicresistance of the cell circuit which includes the resistance of the agarplug; evidently the resistance of the new-cell is of the same order ofmagnitude as that of the conventional mercury pool.

These data show that the new reference electrode, which was handledfrequently during the course of the investigation, performed verysatisfactorily in polarographic analysis. The cell is rugged, reliableand accurate and is very compact, besides being easily handled andpackaged. With the conventional mercury pool electrode, great care hadto be exercised to arrive at equally precise results, but in routinepolarographic analysis, precise results cannot be expected from theconventional electrode.

Although the portable calomel half cell of this invention has beendescribed with particular reference to its use in polarographicanalyses, because of the great importance of having a referenceelectrode in such analyses which is very stable, it is to be understoodthat the portable calomel half cell of my invention may be usedwhereever calomel reference electrodes are needed.

This application is a companion to applications filed by me, Serial Nos.372,411, filed August 4, 1953, and 419,941 filed March 30, 1954.

What I claim is:

1. A portable calomel half cell comprising a closed glass body; atubular container composed principally of fritted glass, said containerbeing completely enclosed in and attached to said body at its upper endand being open at its upper end but otherwise closed, calomel pastesubstantially filling said container, whose upper open end is closed bya porous plug; the fritted glass container and the glass body beingspaced apart to provide an annular chamber within the glass body, saidannular chamber being completely closed; mercury completely filling saidannular chamber; and an electrical conductor passed through a wall ofsaid glass body and entering the space between the fritted glasscontainer and the glass body to make electrical connection with themercury in said space.

2. A portable calomel half cell comprising a hollow glass body which iscompletely closed and sealed; a glass container composed principally offritted glass, said container being completely enclosed in said glassbody and having an opemppper end which is attached to the glass body atthe corresponding end; a transverse partition closing the glass bodynear its lower end; the fritted glass container and the glass bodyhaving no other connection or contact so that there is a closed chamberbetween the fritted glass container and the glass body; an electricalconductor passed through said partition and entering said closedchamber; mercury completely filling said closed chamber; calomel pastesubstantially filling said fritted glass container; and a porous pluginserted in the open upper end of said fritted glass container.

3. A portable calomel cell comprising a hollow tubular body which iscompletely closed and sealed; a glass container composed principally offritted glass, said container being open at one end only and attached tothe tubular body at said open end, said fritted glass container lyingwholly inside said tubular body with its walls spaced from the innerwalls of said body so as to provide a mercury-holding chamber defined bythe inner walls of said body and the outer walls of said fritted glasscontainer; mercury completely filling said chamber; calomel pastesubstantially filling said fritted glass container; a porous pluginserted in the open upper end of said fritted glass container; and anelectrical conductor passed through a wall of said body and making anelectrical connection with said mercury.

4. A portable calomel half cell comprising a hollow glass body which iscompletely closed and sealed; a tubular glass container enclosed in saidglass body but spaced therefrom throughout its length; said glasscontainer being composed of fritted glass for the major portion of itslength but having both ends composed of solid glass, the lower end beingclosed; the upper end of the glass container being open and being fusedto the upper end of the hollow glass body; a transverse glass partitionintegral with said body and closing the lower of the same; an electricalconductor passing through said partition and into the space between saidbody and said container; mercury completely filling all the space between said body and said container; calomel paste substantially fillingthe tubular glass container; and a porous plug closing the tubular glasscontainer and protecting the calomel paste therein.

5. A portable calomel half cell comprising a hollow generallycylindrical glass body having an integral tubular re-entrant portionspaced therefrom and providing a calomel paste container entirely withinthe cylindrical glass body; a transverse wall closing said glass bodynear the lower end, said transverse wall being spaced from the lower endof the glass body and providing therewith a cup-like recess at saidlower end; an electrical conductor; cement filling the cup-like recessand securing the electrical conductor to the hollow glass body; anotherconductor electrically connected to the first-named conductor andpassing through said transverse wall into the space between the glassbody and said tubular re-entrant portion; mercury filling all the spacebetween the hollow glass body and the tubular re-entrant portion; thetubular re-entrant portion having fritted glass walls extending nearlyits entire length but being of glass of the same composition as thehollow glass body at the end thereof which is remote from saidtransverse wall, said end being fused to be integral with the hollowglass body.

References Cited in the file of this patent UNITED STATES PATENTS2,190,835 Gruss et al. Feb. 20, 1940 FOREIGN PATENTS 733,630 GermanyMar. 31, 1943

1. A PORTABLE CALOMEL HALF CELL COMPRISING A CLOSED GLASS BODY; ATUBULAR CONTAINER COMPOSED PRINCIPALLY OF FRITTED GLASS; SAID CONTAINERBEING COMPLETELY ENCLOSED IN AND ATTACHED TO SAID BODY AT ITS UPPER ENDAND BEING OPEN AT ITS UPPER END BUT OTHERWISE CLOSED, CALOMEL PASTESUBSTANTIALLY FILLING SAID CONTAINER, WHOSE UPPER OPEN END IS CLOSED BYA POROUS PLUG; THE FRITTED GLASS CONTAINER AND THE GLASS BODY BEINGSPACED APART TO PROVIDE AN ANNULAR CHAMBER WITHIN THE GLASS BODY, SAIDANNULAR CHAMBER BEING COMPLETELY CLOSED; MERCURY COMPLETELY FILLING SAIDANNULAR CHAMBER; AND AN ELECTRICAL CONDUCTOR PASSED THROUGH A WALL OFSAID GLASS BODY AND ENTERING THE SPACE BETWEEN THE FRITTED GLASSCONTAINER AND THE GLASS BODY TO MAKE ELECTRICAL CONNECTION WITH THEMERCURY IN SAID SPACE.